With bug #110448 (Remove "Memory" page from Options dialog) fixed the corresponding help page needs to be changed: https://opengrok.libreoffice.org/xref/help/source/text/shared/optionen/01011000.xhp As the options are still there, we could turn this into a guide page about modifying these settings (especially with the Quickstarter looking the most "useful"/user visible among them) using the Expert Configuration window.
Olivier Hallot committed a patch related to this issue. It has been pushed to "master": http://cgit.freedesktop.org/libreoffice/help/commit/?id=73f7d3200315ff913d5880d6cc6e392e730c82ef tdf#111083 Memory settings help page is gone too